The present invention relates to an engine ignition coil device.
Japanese Utility Model Publication No. 4-23296 discloses an open-magnetic-circuit-type engine ignition coil device that has a coil case which contains an assembly integrally molded therein by potting with melt insulating resin and consisting of a primary coil bobbin having a hollow interior with a rod-shaped core and a secondary coil bobbin coaxially laid on the primary coil bobbin, and which is further provided with an ignition-plug connector portion integrally formed on the coil case in such a way that tip of an ignition plug inserted therein can be in contact with a high-voltage terminal projecting inwardly into the connector portion of the coil case.
Japanese Laid-Open Patent No. 5-87034 also discloses an engine ignition coil device with an incorporated igniter, which comprises a single cylindrical coil case having an open top and a closed bottom, wherein a primary coil and secondary coil bobbin having a hollow shaft with a core inserted therein is mounted and integrally molded by potting with melt insulating resin and, then, an igniter with an attached thereto heat sink is mounted in an upper portion of the open top end of the coil case, leaving the heat sink exposed outside, and integrally molded therein by potting with melted resin.
The above-mentioned prior art devices, however, involve the following problems to be solved:
The first problem is that an inner assembly of a primary coil bobbin, a secondary coil bobbin, a rod type core and a high-voltage terminal socket may be displaced from a specified position in a coil case while melted resin is poured into the coil case. This results in a problem that the tip of an ignition plug can not properly fit in a high-voltage terminal socket integrally molded in the coil case.
The assembly consisting of the primary coil bobbin, secondary coil bobbin, rod type core and high-voltage terminal socket must be fixed in the required position by using suitable additional means that may require additional parts and additional processing steps. Consequently, the efficiency of manufacturing the ignition coil device is decreased.
The second problem is that the conventional open-magnetic-circuit type engine ignition coil device has a rod-shaped core inserted in a hollow shaft of a bobbin with a primary coil and a secondary coil and, therefore, has a low output-efficiency because the magnetic flux produced can extend outwards and is reduced by iron loss while passing the cylinder head and block of the engine. Consequently, the conventional device necessarily has an increased size to assure a specified secondary output voltage.
Further, the solidified resin layer between the coil case and the inner assembly may suffer thermal-stress cracking that allows current leakage resulting in impairing the resin quality.
The third problem of the conventional device is that an igniter with a heat sink is potted only at its bottom and sides in resin layer in the open top end of a coil case and may come out of the coil case.
In the conventional device, the igniter is mounted in the case independent of a low-voltage terminal socket integrally formed with the coil case. This requires a separate step of wiring between the igniter and the low-voltage terminal, thereby reducing the assembling work efficiency.
The fourth problem is that a conventional engine ignition coil device with an ignition plug directly attached thereto is formed in a single piece and therefore must be prepared in different sizes depending upon the kinds of engines that have different sizes between a mounting seat of an ignition coil device and an ignition plug.